The goal of my research is to assess how climates and environments have changed over the past several thousand years, with the geochemical and sedimentologic analysis of aquatic sediments and archaeological deposits. These environments include estuaries, lakes, coasts, and coral reefs. I utilize environmentally-sensitive isotopes of oxygen, carbon, and strontium, as well as trace elemental concentrations, to evaluate environmental factors such as salinity, streamflow, temperature, ocean circulation, and coastal upwelling. One of my primary field areas is the San Francisco Bay estuary and watershed, where I have worked over the past ten years with three graduate students and one postdoctoral fellow. Projects are aimed at addressing the following questions: (1) What was the natural variability of annual average inflow into the San Francisco Bay estuarine system during the Holocene and the last interglacial? (2) What was the amplitude and seasonal distribution of inflow during this period? (3) How did changes in inflow and sea level rise affect the ecosystems of the northern reach of the estuary? 4) What are the implications for future climate change and sea level rise for the San Francisco Bay system and other urban estuaries? (5) How has upwelling along California coast varied over the past several thousand years? One of the primary goals of this research is to produce a long-term record of salinity and streamflow to the bay, to provide a context in which to evaluate recent natural and anthropogenic changes. We are analyzing both changes in annual average inflow as well as seasonal salinity changes, using variations in _18O along growth increments of individual mollusk shells from cores taken within the estuary, and from stratified native American shell mounds from the shores of the bay. These data will allow us to reconstruct historical changes in intra-annual variability of the San Francisco Bay. Of particular interest will be variations in the seasonality of freshwater inflow to the estuary, which would by indicative of corresponding variations in precipitation over the watershed. A related project in the San Francisco Bay watershed aims at developing a method for distinguishing juvenile salmon stocks by examining the concentrations of trace elements and isotopic compositions (both Sr isotopes and stable isotopes) along sequential growth layers of otoliths (aragonitic ear bones) and scales. Salmon populations have recently declined in the rivers that drain into San Francisco Bay. This decline may be caused by water development (upstream storage-dams and reservoirs), water diversion, and delta pumps, which cause pump mortality of young fry. To offset the declines of salmon populations, it is critical to distinguish between the various races of salmon that populate the different rivers. Salmon reared in these rivers should carry a chemical "fingerprint" of the watershed from which they originated.

In another research project we are developing a geochemical technique detecting ancient coral bleaching events, and causitive environmental conditions, in French Polynesia and the Great Barrier Reef. Coral reef bleaching has been reported since the late 1800’s on reefs worldwide, although this phenomenon appears to be increasing in frequency, possibly due to anthropogenic disturbances, over the past few decades. We wish to establish a long-term (several hundred year) record of coral bleaching and sea surface temperature and salinity, in order to evaluate whether bleaching events are in fact increasing in frequency over the past century, and which environmental factors may be causing the bleaching events.